Numerous schemes have been proposed to make radio communications relatively immune to interference and secure from undesired listeners. A simplistic technique for securing such communications is through use of a standard audio encryption system on a conventionally transmitted signal, and use of a corresponding decryption system once the signal is received. A more sophisticated technique, known as spread-spectrum transmission, relies on transmission of an information signal over a wide range of frequencies, using temporal frequency-hopping, broad-band modulation, or other well-known mechanisms.
One encryption scheme, taught in U.S. Pat. No. 5,048,086 to Bianco et al, employs the mathematical theory of chaos by encrypting data with a chaotic equation known as the logistic difference equation.
Other chaotic systems are discussed in L. M. Pecora and T. L. Carroll, Synchronization in Chaotic Systems, 64:8 PHYSICAL REVIEW LETTERS, p. 821 (Feb. 19, 1990) and in T. L. Carroll and L. M. Pecora, Synchronizing Chaotic Circuits, 38:4 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS, p. 453 (Apr. 1991). These articles disclose a theory of synchronizing two chaotic systems, describe a circuit demonstrating such synchronization, and suggest as an application the linking of two remote systems, each with internal signals behaving chaotically, yet in synchronization with each other.
None of the known teachings, however, provides a practical application for synchronized chaotic systems. Ideally, chaotic techniques could be applied to communications systems to provide relatively simple means for achieving robust and secure communications.